1. Field of the Invention
Embodiments of the present invention relate to an optical device, and more particularly, to an optical output control device.
2. Description of the Related Art
In general, optical devices are very vulnerable to excessive changes in current. Laser diodes that are currently being developed are primarily used in optical devices, commonly for laser printers. Different models of laser diodes have different optical power output. Even when laser diodes are rated as having the same optical power, if the manufacturers of the laser diodes are different, circuits for monitoring the output power of the laser diodes may also be different. Such differences in monitoring circuits are standing in the way of standardizing and simplifying optical power monitoring circuits.
FIG. 1 is a general block diagram of a light control and feedback circuit. Referring to FIG. 1, the circuit includes an optical power monitor 100 monitoring light emitted from a laser diode and converting the monitored light into a current, a variable resistance for optical power control 120 controlling the size of the current, an optical power compensating unit 140 compensating for an optical power using the current whose size has been controlled by the variable resistance 120, and an operational current varying unit 160 increasing or decreasing the operational current supplied to the laser diode, according to a result of the optical power compensating unit 140.
FIG. 2 is a block diagram illustrating a conventional configuration of an optical output controller. As illustrated in FIG. 2, the conventional optical output controller includes a laser diode 200 emitting laser light, a photodiode 210, which is a photo detector sensor, receiving monitoring light from the laser diode 200 and converting the received light into a current signal, and an automatic power controlling unit (APC) 220 controlling a light power supplied to the laser diode 200 in accordance with a feedback current from the photodiode 210.
In FIG. 2, an output current of the photodiode 210 is input into the automatic power controlling unit 220 to control an output power of the laser diode. To control an amount of the feedback current supplied to the automatic power controlling unit 220, for controlling the output power of the laser diode, a resistance circuit can be utilized. The resistance circuit can include a load resistance (RA) to protect the laser diode from overly large variations in current, caused by a variable resistor (VR), static electricity, and so on.
As shown in FIG. 2, the optical output controller obtains information necessary to control the output of light from the laser diode in a predetermined direction toward a desired optical system, from some of the light detected by the photodiode 210. The photodiode 21 can include a light intensity sensor checking a state of the light source power. In addition, if necessary, the optical output controller can control an optical power by controlling the amount of driving current supplied to the laser diode 200. In particular, since a variable resistance device capable of manually controlling optical power is attached to a feedback resistance circuit, controlling the optical power, the feedback resistance circuit can control the initial light intensity setting, e.g., during manufacturing of the optical output controller, by controlling the variable resistance device.
That is, by controlling an amount of monitoring current flowing through a variable resistance (VR), the amount of feedback current can be changed, and thus, the amount of operating current supplied to a semiconductor laser can be changed.
Meanwhile, in the optical output controller of a conventional optical device, if optical power specifications of a laser printer model are changed, a value of the variable resistance or fixed resistance should accordingly also be changed. This means that a new circuit should be formed and tested, which increases manufacturing costs. In other Words, the maximum variable range of the variable resistance changes according to the optical power specifications, for proper operation of a semiconductor laser. Thus when the specifications of a semiconductor laser, and the manufacturers of its components, are changed, a variable resistance also has to be changed, which is inconvenient. Further, even components having identical optical power specifications cannot be directly exchanged with one another due to a range of differences between variable resistances caused by different monitoring current ranges for an optical power.
Meanwhile, during the manufacture of the optical output controller, an operator controls the variable resistor of the optical output controller manually such that the optical device outputs a required optical power. Here, the variable resistor is very sensitive to manual handling. That is, the operator intends to maintain a required optical power by manually controlling the variable resistor. However, if the operator rotates the variable resistor more than necessary, an excessive current may be temporarily applied, and thereby an optical device, such as a laser diode (LD), can be damaged. Such damage is usually not serious enough to be detected when a laser printer, including the optical output controller, is shipped, however, as the laser printer operates, degradation of the included optical device occurs, which eventually results in deterioration of the laser printer.